Heating roller

ABSTRACT

A heating roller for web-like materials, in particular paper has a cylindrical roller body with at least one flange journal. At least one feed line and/or discharge line for a heating medium, in particular steam, are provided. Several, at least, approximately axially aligned and, preferably, disposed peripherally, lines and/or bores pass the heating medium through the roller body. At least one collecting chamber is formed within the heating roller.

FIELD OF THE INVENTION

The present invention pertains to heating roller used for processingweb-like materials, e.g. paper.

BACKGROUND OF THE INVENTION

Heating rollers for web-like materials consist of a cylindrical rollerbody, at least one flange journal, at least one feedlline and/ordischarge line for a heating medium, e.g. steam, and peripheral bore,lines or passages for passing the heating medium through the rollerbody. These rollers have a more or less solid roller body into which alarger number of axial bores have been made mostly near the rollersurface, i.e., peripherally, a heating medium flowing through theseperipheral bores and/or lines and transferring its thermal energy to thewalls of the bores and/or lines and thus to the roller surface.

Another type of roller has a tubular roller body, in which the heatingmedium is passed through the hollow interior of the roller body,transferring its thermal energy to the interior of the roller body.

A significant difference between these two known types of heatingrollers consists in that the heating roller type of the type firstdescribed above can certainly be used for liquid heating media such aswater and thermal oil, but so far have not been used with an especiallyadvantageous thermal transfer medium, namely steam.

This is due to the fact that steam condenses at least partly within thebores and/or lines, and transfers a great portion or all of its heat tothe roller body, the roller surface and thus to the web-like material tobe processed. The resultant condensate is pressed outwards due to thecentrifugal forces mostly occurring in paper working machines, e.g.release super calenders, etc. into the bores and/or lines so that thecondensate cannot flow off. Due to this, the bores are increasinglyfilled with condensate during operation until, finally, the entire boresare closed by water. Due to this, the flow rate of steam and, inparallel, the heating are practically reduced to almost zero. The knownheating roller of the type first described above would have to bedecelerated in this case to such an extent that the centrifugal forcesare no longer sufficient for retaining the water in the bores and/orlines. In the extreme case, this type of roller would even have to bestopped in order to allow the condensate to flow off at least from thebores which are positioned at the top. It is obvious that situationsoccur at any rate both during the obstruction process and during thesubsequent decelerating and emptying processes, which result in aheating roller of this type being heated non-uniformly so that irregulartemperature profiles occur along the heating roller which lead tothermally caused deformation and distortions, etc.

For these reasons, steam has not been used as a heating medium for thistype of roller. However, steam is an ideal heating medium, since italways condenses preferably at those locations within the roller andtransfers its heating capacity to those locations which are the coldestlocations. Thus, it is ensured by this property of the heating mediumitself that there is always an approximate or uniform temperatureprofile across the surface which is essential for the treatment of theweb-like material, or at the least, across the entire surface of theheating roller.

As opposed to this, the use of steam in the other type heating rollersdoes not present any problems, since the remaining condensate can beremoved from the roller in known fashion either via a commerciallyavailable upright siphon or one rotating with the roller.

However, the roller of the type first described above has a decisivecost advantage as compared with the roller of the second type, namely,inasmuch as the heating rollers of the other type have a very largehollow space located in the roller body, and, for this reason, aresubject to especially complicated acceptance conditions in manycountries, e.g. in the USA, because they are considered to be pressurevessels. It must be borne in mind that the steam pressure is about 20bar at a temperature of about 211° C. and is about 40 bar at atemperature of about 249° C. However, these complicated acceptanceconditions do not apply to vessels having an internal diameter of lessthan 6 inches, i.e. less than about 152.4 mm., each of the individualaxial bores and/or lines of the roller type first described above beingconsidered as an individual vessel in the definition of the vessel.

Thus, consequently the advantage is that, with constant quality,functionality and operational safety, a roller of the type firstdescribed above can be produced and offered for sale at much lesser costthan a roller of the other type.

Moreover, the following must be taken into consideration: In order tocomply with the line pressures which must be relatively high, e.g. inrelease supper calenders, namely up to about 450 or even 500 kN/M and,in individual cases, even higher, steel must be used as the material forthe heating rollers, because for reasons of heat transfer to the paper,the roller wall must be as thin as possible. Moreover, the roller wallmade of steel can be surface-hardened. However, the production cost forproducing heating rollers of the other type is increased because of thespecial acceptance conditions.

SUMMARY OF THE INVENTION

The invention relates to a heating roller for web-like materials, inparticular paper, which comprises a cylindrical roller body and at leastone, preferably two, flange journals, which are respectively connectedto opposite ends of the cylindrical roller body. At least one feed lineand/or discharge line for a heating medium extends through at least oneof the flange journals. The heating medium, in particular steam, ispassed through at least one at least approximately axis-parallel,preferably peripheral bore or line through the heating roller. The boresand/or lines are preferably connected to at least one connecting chamberand/or at least one connecting line with the feed lines and/or dischargelines.

It is the object of the present invention to further develop a roller ofthe type first described above in such fashion that it can at leastsubstantially eliminate the disadvantage of the heating roller of theprior art. In particular the roller first described above is furtherdeveloped in such fashion that it can be operated at least partly with agaseous heating medium, in particular steam.

The advantages attainable with the present invention are based on thefact that at least one collecting chamber for receiving the condensateof the heating medium, preferably steam, is disposed in the heatingroller.

Due to this it is possible to also use the roller type first describedabove for steam, since operating centrifugal forces press the condensateinto the correspondingly disposed collecting chamber, from where thecondensate, preferably water, can be discharged.

Thus, heating rollers for super calenders or release super calenderswhich are preferably operated with steam, can be designed for use withthe roller of the type first described above which because of thecomplicated and costly acceptance conditions and the requirementsregarding the rollers, can no longer be used.

Moreover, steam is present in any customary paper mill so that in thecase of a direct steam heating an additional heating station with heatexchanger for converting steam energy to hot water and a separatecirculation pump can be dispensed with.

Moreover, the essential advantage of the roller of the type firstdescribed above, is that the bores and/or lines are located very closeto the roller surface so that the heat transfer is very advantageous.Since the bores have an inner diameter of less than 6 inches or 152.4 mmthe steam-carrying bores and/or lines are not longer considered aspressure vessels, thus the expensive steel mostly used in connectionwith the stringent acceptance conditions can be eliminated and moreeconomy-priced chill castings can be used.

The roller according to the invention provides a much higher surfacetemperature than a positive-displacement roller, i.e. a roller of thetype, with a given steam temperature.

Steam is almost always available in manufacturing facilities up topressures of about 10 bar, i.e. approx. 180 ° C., and thus is not aproblem

Moreover, the amount of condensate present in the roller of theinvention is extremely low so that, compared with a heatedpositive-displacement roller, the risk potential of the roller accordingto the invention is small.

Since there is no temperature drop of the heating medium, in particularof the steam, occurring as it passes through the roller body there is acompletely balanced temperature profile at least across the areaaccessible to the web-like material, and, preferably across the entireroller area.

The controllability of the heating capacity of the heating rolleraccording to the invention is extremely variable and can be adjustedfrom zero up to a maximum heating output.

The sealing heads for the flange connections, which are necessary forthe heating roller according to the invention, can be much smaller,since, for example, the resulting condensate is only about 3 1 perminute with a heating output of 100 kW. Moreover, it is not necessary toadditionally load the sealing heads with the dynamic pressure of a pumpdisposed within the circuit for a heating medium. Ultimately, noadditional energy requirements are needed for the heating and/or themovement of the heating medium. Very high temperatures connected withcorrespondingly high pressures can be employed with the heating rolleraccording to the present invention. Since sealing heads are availablewhich can be loaded up to 17 bar, temperatures of about 207° C. can beput into practice without any problems.

The collecting chamber can advantageously comprise a peripheral annularchamber at at least one of the axial end portions of the roller bodyand/or in the area of at least one of the flange journals. This annularchamber is disposed in such fashion with respect to the bores and/orlines that the centrifugal forces cause the condensate accumulatingwithin the bores to be forced into the peripheral annular chamber(s),from where the condensate, in particular water, can be easilydischarged.

An annular chamber can be advantageously allocated to each bore in orderto receive the condensate via the effect of the centrifugal force.

Each of the collecting chambers regardless of design can advantageouslybe connected via a discharge, e.g. in the form of at least one bore orat least one tube, to a discharge opening for the condensate. Thisdischarge opening for the condensate may be identical to the feed lineand/or discharge line for the heating medium, in particular steam butshould at any rate be provided in the end portions of the heating rollerand in particular through one or both of the flange journals of theheating rollers.

In order to achieve an additionally increased uniformity of thetemperature profile across the roller body, a bore parallel to the axisof the roller, as a rule a centric bore, may be provided through theroller body, through which the heating medium, in particular steam, ispassed to the other end of the heating roller and/or roller body so thatuniform amounts of steam with a uniform temperature can act from bothsides of the roller body.

The temperature of the heating roller according to the invention isadvantageously controlled via the amount of the condensate discharged.Such a control can be carried out via a valve means which, according tothe invention, can be disposed outside the heating roller.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partial longitudinal section through an end portion of aheating roller according to the invention.

FIG. 2 is a partial cross-section of an end portion of a heating rolleraccording to the invention.

FIG. 3 is a schematic flow diagram showing steam supply and condensatedischarge for a heating roller in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a heating roller for web-like materials, inparticular paper, which comprises a cylindrical roller body and at leastone, preferably two, flange journals, which are respectively connectedto opposite ends of the cylindrical roller body. At least one feed lineand/or discharge line for a heating medium extends through at least oneof the flange journals. The heating medium, in particular steam, ispassed through at least one at least approximately axis-parallel,preferably peripheral bore or line through the heating roller. The boresand/or lines are preferably connected to at least one connecting chamberand/or at least one connecting line with the feed lines and/or dischargelines.

It has not been possible with rollers, other than the type firstdescribed above, heated with steam to control the temperature of theroller by throttling the amount of steam without obtaining an extremelyirregular temperature profile. Throttling leads to a pressure drop inthe roller, because the reduced amount of steam introduced into theroller condenses immediately at the first cold point so that the remoteareas are no longer provided with sufficient thermal energy.Consequently, these remoter areas remain cooled, and a completelynon-uniform temperature profile is obtained. At the same time, largedeviations in the temperature of the circumference of the roller areconnected, which can be within the range or beyond the range of thethickness of the web-like material to be treated.

It is not possible with the rollers of the invention to simply throttlethe steam supply. According to the invention, control of the condensatedischarge via a valve outside the roller makes it possible to controlthe roller temperature uniformly across the entire temperature range upto the maximum temperature of the heating roller.

The bores and/or lines (passages) disposed near the surface of theroller are filled with condensate and/or water, which is not, or onlypartly, discharged. In this fashion, the amount of water held in thebores increases, and the free surface of the bores which is capable ofreceiving the heat from the condensing steam decreases. In this fashion,the roller can receive a smaller amount of heat with an increasingamount of condensate in the bores and/or lines so that the thermaloutput of the roller according to the invention can be controlled bymeans of the amount of condensate being discharged. In order toestablish a path for the condensate, the bores and/or the lines may beinclined slightly from the center towards the outside. The bores and/orlines can either deviate by about 1 to 100 mm from parallel to the orextend in parallel fashion towards the center.

Advantageously, at least one of the collecting chambers can comprise atat least one end of the bores and/or lines and/or a respective bore orline and a pocket can be designed with a circular cross-section with adiameter preferably smaller than the diameter of the peripheral bore,and the pocket may be offset towards the outside with respect to theperipheral bore and/or line. Due to this, the condensate located in thebores and/or lines near the roller surface is prevented from flowing ina gush from the bores and/or lines in the upper portion of the rollerthrough the steam-supplying connecting lines and/or connecting boresinto the bores and/or lines of the lower portion of the roller, if thecentrifugal forces acting on the condensate are no longer present. If,the roller according to the invention is stopped to change a paper roll,when the roller is standing still, an excessive mount of the condensatecannot accumulate in the lower portion of the roller in order to createan irregular temperature profile in the diameter of the roller and/orthe circumference of the roller so that distortion and warping of theroller body can be prevented. The steam lines must of course be arrangedin such fashion that they open into the collecting chamber in such a waythat there is an obstacle for the condensate which would otherwise flowoff.

On the other hand, when peripheral bores and/or lines (passages) aresubstantially parallel to the axis of the roller during operation of theroller the condensate flows to the collecting and/or annular chambers orpockets in such fashion that there are no obstacles for the condensateflowing from the bores into the annular chamber and/or the pocket.Connection to the discharge should be provided, e.g. in the form of atleast one bore or at least one tube, in such fashion so that nocondensates can be formed. There is should be no substantial flowrestriction for the condensate flow within the discharge lines.

On the other hand, according to the invention, it should be possible todischarge the entire amount of condensate from the roller duringslow-speed operation of the roller or during periods when the rollerstands still.

In as much as larger amounts of condensate are obtained during theoperation of the roller according to the invention, it may beadvantageous to provide a retention means, preferably a non-returnvalve, flap traps or the like within the bores and/or lines and/orwithin the connecting chambers or the connecting lines at the endportions of a respective bore and/or line, which retain the condensateat least substantially if the roller runs slowly or stands still, inorder to prevent condensate accumulations in the lower portion of theroller which could lead to a non-uniform temperature profile and thus todistortion or warping of the roller.

In order to thermally uncouple amounts of condensate accumulating in thecollection chamber and/or the collecting chambers from the rollersand/or bores or lines and thus from the roller body, the end portions ofthe bores adjoining the respective collecting chambers should besurrounded by heat-insulating material.

The roller designed according to the invention cannot only be used forthe release super calenders mentioned above, but also in so-called glossor soft calenders, in which one or several plastic-coated rollers pressthe paper web against a heated roller, the surface temperature of theroller not having to be higher than about 160° to 170° C.

The outstanding advantage of the roller according to the invention is,as mentioned above, that in each of the bores and at each point of thebores and/or the roller body there is an almost identical steam pressureand thus also almost the same temperature. Even the smallest temperaturedeviations along a bore and/or along the roller body result in increasedsteam condensation at that point, thus the steam gives off a largeportion of its energy during condensation, and the temperature is thusagain balanced at this point. Much less steam condenses at adjacentpoints so that a portion being too cold is automatically heated.

According to the invention, it may be advantageous for the heating ofthe heating roller to use steam to control the temperature of theentering steam by the fact that a moistening follows a throttling of thesteam pressure. In this fashion, the steam which can be passed into theheating roller can be enriched or even saturated with moisture so thatin the latter case the heating steam is present as wet steam.

Temperature differences occur in all other rollers during the passage ofthe heating media through the heating rollers due to the emission ofheat from the heating medium and the resultant cooling of the heatingmedium as it passes through the roller body. This makes treatment of theweb material non-uniform due to the differing temperatures and, leads todimensional changes of the roller which also has a disadvantageouseffect on the web material.

The heating roller designed according to the invention is in generaldesignated with the reference numeral 10 in FIG. 1. The roller 10comprises a flange journal 12, preferably on each side, and acylindrical roller body and/or roller shell 14 whose surface 11 is usedfor the pressure-processing of a web-like material, in particular paper,synthetic material or the like. A heating medium is introduced into theheating roller 10 via a feed line extending through the flange 12.

In the embodiment represented in FIG. 1 the steam is introduced intoconnecting lines 24, via the feed line 36. Part of the steam from feedline 36 is passed via line 20 disposed parallel to the axis of and inthe central portion of the roller 10 to the other end of the heatingroller 10. The steam enters the collecting chamber 28 via the connectingline 24. Steam condensate can accumulate in chamber 28 during operationof the heating roller 10 when sufficient centrifugal forces occur.

The collecting chamber 28 is disposed adjacent to the bores and/or lines(passages)16. Bores and/or lines 16 may be substantially or nearlyparallel to the axis of roller 10. One collecting chamber 28 may in eachcase be allocated respectively to one bore and/or line 16. On the otherhand, or additionally, a peripheral annular-shaped collecting chambercould be allocated to all bores 16.

In the present case, the collecting chamber 28 is provided in the flange12 connected to the roller body 14 by means of fastening means 32.

The axis of collecting chamber 28 is offset with respect to the centralaxis of the respective bore 16. Due to this offset, condensate flowthrough the connecting line 24 into the lower portion of the heatingroller 10 can be prevented during the slow-speed operation of standstillof the roller, whereby non-uniform temperature profiles, changes in thediameter of roller 10 and a detrimental effect on the material to beprocessed may not occur. Due to the design of the collecting chamber 24with a smaller diameter and axial displacement an obstacle 38 is formed,which prevents the the condensate from flowing out of bore 16 via thefeed line 24.

A part of the steam is passed to a corresponding arrangement on theopposite side of the heating roller 10, which is shown in FIG. 1 and/orFIG. 2 due to the bore 20 being disposed concentrically or parallel tothe axis within the heating roller 10. Steam is introduced into theentire length of the bores and/or lines 16 and thus into the roller body14 in order to achieve in this fashion a still more uniform temperatureprofile.

Insulation 30 is disposed in the marginal area and/or the end area ofthe bores 16 in order to bring about a thermal uncoupling of thecondensate which may be contained within the collecting chamber 28.Additional insulation may be provided in the boundary area between theflange journal 12 and the roller body 14, e.g. on the side of the flowobstacle 38 pointing towards the roller body 14.

In order to ensure the discharge of the condensate during operation atleast one bore and/or a tube 26 is provided which is connected to thecollecting chamber 28. The condensate is conveyed from the collectingchamber 28 into a condensate collecting chamber 22 via orifice 27 intube 26 and from there into a condensate discharge line 18. Theconveying of the condensate can be effected via the stream pressure orvia a partial vacuum applied to the chamber 22 and thus to the line 18.In order to arrange the tube 26 in the flange 12 a radial duct may bedrilled in the flange 12. The tube 26 may be pushed into this radialduct and tube 26 can be closed towards the outside of flange 12 by meansof a seal fixed within the duct.

The tube 26 has an opening or orifice 27 which is positioned, ifpossible, near the outer end of the collecting chamber 28 so that itdoes not form any obstacle for the condensate.

Retention means such as a non-return valve or the like may be providedin the end portion of the bore 16 and/or in the area of the collectingchamber 28 in order to prevent the condensate from flowing out ofchamber 28 and an accumulation of this condensate in the lower portionof the roller 10 in the case of a standstill or a slow-speed running ofthe roller. In this case the flow obstacle 38 according to FIG. 1 is notimperative so that the connecting line can open directly into the bore16 without having a direct connection with the collecting chamber 28.

Annular chambers may also be provided at the roller ends to supply steamto each peripheral bore 16 and for the discharge of the condensate fromline 18. Annular chambers will replace feed line 24 and tubes which areconnected to all peripheral bores 16 for the distribution of the steamand discharge of the condensate.

A valve means may be provided outside the roller 10, which adjoins theline 18, via which the condensate discharge and thus the temperature ofthe roller can be controlled. The condensate can be withdrawn via theaforementioned flow path, driven by the centrifugal force and/or thesteam pressure and/or a suction applied from the outside.

The condensate collecting chambers 22 may also be located in the flangejournals via which the condensate can get into the discharge line 18.

If the line 18 is not used it is advantageous if the steam can be passedvia the feed lines and/or discharge lines 26 provided in flange journals12.

A partial cross-section through a heating roller designed according tothe invention is shown in FIG. 2, which again shows the position of thecollecting chamber 28 for the condensate which is offset with respect tothe borer and/or the line 16.

As for the rest, the elements represented in FIG. 2 have the samereference numerals as the elements represented in FIG. 1.

The required elements such as the collecting chamber 28 and the elementsconnected with the tube 26 are not represented in the connecting line 24which is obliquely disposed with respect to the vertically orientedconnecting line 24 in order to emphasize the required elements connectedwith the vertically aligned connecting line 24.

A possible flow circuit for the roller 10 according to the invention isrepresented in FIG. 3. The supply of heating medium and/or steam to theheating roller 10 according to the invention can be controlled via thefeed line 40 and a shutoff valve 42 disposed in the feed line 40. Thesteam introduced into the heating roller 10 is preferably partlymoistened or completely saturated after a pressure relief so that thesteam supplied to the heating roller 10 is saturated steam or wet steam.The foregoing embodiment suggests that the steam is supplied via oneflange journal of the roller 10, and the condensate with and/or withoutthe steam portion is withdrawn from the opposite flange of the heatingroller 10 according to the invention. Both operations or steps could, ofcourse, be performed via the same flange of the heating roller 10according to the invention. A discharge line 44 for the condensatepossibly with steam admixture is provided on the discharge side. Thecircuit includes a condenser 46 which works in known fashion. A bypassvalve 48 is disposed in parallel to the condenser 46 and may beprovided, e.g. for safety purposes. Moreover, the circuit includes acondensate control valve 50 for a heating medium for the heating roller(10) according to the invention, by means of which the amount ofcondensate withdrawn from the heating roller 10 can be controlled. Dueto this, continuous control of the temperature of the heating roller 10is brought about by adjusting the discharge of the condensate in thebores and/or lines 16 near the roller surface of the heating roller 10to a high rate. If too much condensate is withdrawn, i.e. if thecondensate control valve 50 is completely open, the steam introducedinto the heating roller 10 can completely give off its thermal energy tothe surface of the bores 16. If, on the other hand, the condensate isonly partly discharged, a large portion of the surface of the bores 16is completely occupied by condensate and is not accessible to the steamso that the steam can only give off its thermal energy to parts of thesurface of the bores 16. If the condensate control valve 50 iscompletely closed, no condensate flows off, the bores get clogged andthe steam passage is suppressed. In this case, the heating roller 10cools rapidly together with the condensate contained therein.

What is claimed is:
 1. A heating roller for web-like materials, inparticular paper, comprising:cylindrical roller body, at least oneflange journal, at least one feed line and discharge line for a heatingmedium, in particular steam, several, at least approximatelyaxis-parallel, preferably peripheral passages for passing the heatingmedium through the roller body, the improvement comprising at least onecollecting chamber disposed within the heating roller at the ends of theperipheral passages in order to receive the condensate formed by thecondensation of the heating medium, preferably steam.
 2. A heatingroller according to claim 1 wherein at least one of a connecting chamberand connecting line is provided for the passages.
 3. A heating rolleraccording to claim 2, wherein each collecting chamber comprises acircumferential annular chamber in at least one axial end portion of oneof the flange journals in the area adjacent said roller body.
 4. Aheating roller according to claim 3, wherein a collecting chamber isallocated to each passage.
 5. A heating roller according to claim 4wherein a discharge, in the form of at least one of a bore or tube isprovided, which corresponds to one of a respective collecting andannular chamber.
 6. A heating roller according to claim 5, wherein aline is provided within the roller body in order to pass the heatingmedium to one of another end of the heating roller and the roller body.7. A heating roller according to claim 6, wherein discharge of thecondensate can be controlled by a valve means.
 8. A heating rolleraccording to claim 7, wherein at least one of the passages is one ofinclined towards the central axis of the roller about 1 to 100 mm fromaxial parallelism or extends exactly in axis-parallel fashion.
 9. Aheating roller according to claim 8, wherein at least one of thecollecting chambers comprises at least at one end of the passages agenerally round pocket, which has a diameter being smaller than thediameter of the passage, the pocket being outwardly offset with respectto the passage.
 10. A heating roller according to claim 9, whereintemperature control can be carried out by means of pressure control ofthe steam with subsequent moistening of the steam.
 11. A heating rolleraccording to claim 9 wherein six, at least approximately axis-parallel,peripheral passages are disposed.
 12. A heating roller according toclaim 10, wherein a retention means, selected from the group comprisinga non-return valve, or flap trap for retaining the condensate isdisposed in one of the connecting chamber or connecting lines at the endportions of the respective passage.
 13. A heating roller according toclaim 12, wherein the end potions of the passages are provided with aheat-insulating material.
 14. A heating roller according to claim 13,wherein at least one constriction is provided in the end portions of oneof the approximately axis-parallel passages in order to retaincondensate in particular if the roller stands still.